The present invention relates to a mixing apparatus and, more particularly, to a pug mixer for mixing relatively viscous batches of material such as industrial waste being mixed with stabilizing and neutralizing agents.
Waste materials such as those produced by industry, as well as those excavated from existing contaminated disposal areas, often require treatment prior to final disposition. Such treatment includes combining the contaminated material with the necessary cementitious ingredients and/or other chemical additives to create a homogeneous material which, when solidified and/or neutralized, will prevent the contaminants from migrating into the environment.
The requirements for treating the waste materials are widely varied depending upon the consistency and chemical nature of the materials. For example, the materials may be dry and uniformly graded, such as arc dust generated by steel producers in the operation of carbon arc furnaces, sticky clay, such as result from the use of earthen materials to retain waste chemicals or paint residues collected from the filter systems of coating operations, while others may be in the form of fluids as well as in the form of solid materials such as plastic and paperboard containers. Other loads discharged at the treatment facility will include a plastic slip sheet or truck body liner that has protected the body of the truck during shipment.
To accomplish the proper blending of contaminated material with neutralizing chemical agents, it is necessary to accurately proportion the materials and homogenize each constituent material for the time and speed required to complete the proper transformation to a composite non-toxic or less toxic material, acceptable for final disposal.
Since each different material requires a different method of treatment including varying mixing times and different proportions of waste material to the neutralizing/ stabilizing agents, it is impractical to provide a continuous flow mixing system to process these waste materials. It has been found that such a mixing operation is best performed using a batching procedure wherein a given quantity of the waste material is mixed in each batch and in which the residence time of the material in the mixer may be adequately controlled to effect the proper chemical change in the material.
While many prior art batch-type mixers have been proposed, such mixers typically include an opening in the top of the mixing box or bin through which material may be loaded into the mixer, and an aperture in a lower part of the mixer with a closure member wherein the closure member may be moved to allow the material to discharge out of the bottom of the mixer. Such a mixer is disclosed in U.S. Pat. No. 3,853,305 to Mize and may be subject to leakage of fluid materials past the sealing points between the closure member and the bottom aperture in the bin. In addition, any seals which are provided at the sealing point between the closure and the aperture may be subject to deterioration as a result of contact with corrosive materials such as are typically found in hazardous wastes.
U.S. Pat. No. 3,563,515 to Chapman discloses another mixing machine for mixing batches of material in which the material is both loaded and unloaded through an aperture in a top portion of the mixer. This mixer is provided with means for tilting the mixer from an upright position to empty the material therein and includes lightweight hydraulic motors to facilitate the tilting operation. The mixing bin of the unit must be mounted at a high enough elevation for it to empty into a container of a desired height and such an arrangement may not be practical where the materials are intended to be emptied into the bed of a large capacity receiving bin having high side walls.
Other problems with prior art of mixers include typical difficulties associated with mixing non-homogeneous material wherein the blades of the mixer jamb as they encounter large bulk pieces of foreign material. Such a jamming situation may result in breakage of the blades or breakage of any gears in the transmission mechanism of the blade drive shafts.
In addition, prior art mixers have not provided means for adjusting the relative rotational position of one set of blades to the other such that a desired shear effect may be obtained depending upon the viscosity of the material being mixed. Nor have prior art mixers provided means whereby an acceptable stabilized material may be produced en masse from a formula developed in the laboratory for each specific waste stream. Such an apparatus would require means for weighing a specific amount of first material which requires homogenizing in the mixer for a given period of time prior to adding a specific weight amount of a second material, and further providing means whereby the first and second materials may be blended over a given or extended period of time to effect the proper chemical change prior to adding additional materials.
Accordingly, there is a need for a mixer which may be easily loaded with material and unloaded without the need for a movable closure element which may be subject to failure and leakage. There is also a need for a mixer in which the height of the mixer may be adjusted appropriately to accommodate various loading and unloading devices without requiring time consuming adjustments to the mixer structure.
Further, there is a need for a mixer shaft drive system and control means wherein the velocity and relative rotational position of the mixer shafts to each other may be controlled in accordance with the particular material being mixed in addition to being readily stopped upon material jamming the blades.
Finally, there is a need for a mixer having the ability to accurately measure the quantity of different added materials, and being able to mix the different materials together at a velocity and duration sufficient to cause a predetermined chemical transformation.